Self developing photographic film assemblage

ABSTRACT

A PHOTOGRAPHIC FILM ASSEMBLAGE OF THE SELF-DEVELOPING TYPE COMPRISING A PHOTOSENSITIVE LAYER ON ONE OF A PAIR OF SHEETS INCLUDING A RECTANGULAR AREA ADAPTED TO BE EXPOSED AND PROCESSED BY SUPERPOSING THE SHEETS AND ADVANCING THEM RELATIVE TO AND BETWEEN A PAIR OF JUXTAPOSED PRESSURE-APPLYING MEMBERS TO DISTRIBUTE A VISCOUS LIQUID PROCESSING AGENT IN A THIN LAYER BETWEEN THE SHEETS FROM THE LEADING EDGE OF THE EXPOSED AREA TO THE TRAILING EDGE THEREOF. THE ASSEMBLAGE INCLUDES SPACING LAYERS AT THE LATERAL MARGINS OF THE AREA, TAPERED IN THICKNESS FROM A MAXIMUM NEAR THE LEADING EDGE TO A MINIMUM NEAR THE TRAILING EDGE OF THE AREA. A PREFERRED EMBODIMENT SHOWN IS A SELF-DEVELOPING FILM UNIT COMPRISING TWO RECTANGULAR SHEETS SECURED IN FACE-TO-FACE RELATION BY A BINDING SHEET SECURED TO THE SURFACE OF ONE OF THE SHEETS AND HAVING MARGINAL SECTIONS FOLDED AROUND THE LATERAL AND TRAILING END EDGES OF THE SHEETS AND SECURED TO THE MARGINS OF THE OTHER SHEET. THE BINDING SHEET IS FORMED WITH A RECTANGULAR OPENING THROUGH WHICH A LAYER OF PHOTOSENSITIVE MATERIAL BETWEEN THE SHEETS IS EXPOSED AND/OR A VISIBLE IMAGE FORMED BETWEEN THE SHEETS IS VIEWED. THE BINDING SHEET INCLUDES A SECTION TAPERED IN THICKNESS FROM AT LEAST THE LEADING EDGE OF THE OPENING TO AT LEAST THE TRAILING EDGE OF THE OPENING FOR COOPERATING WITH THE PRESSURE-APPLYING MEMBERS TO CONTROL THE THICKNESS OF THE LAYER OF LIQUID AND IS FORMED OF A UNIFORMLY THICK SUPPORT AND A PIGMENT-CONTAINING COATING WHICH IS TAPERED IN THICKNESS.

Sept 25, 1973 v H LAND ET AL 3,761,268

SELF-DEVELOPING PHOTOGRAPHIC FILM ASSEMBLAGE Filed May 5, 1972 2 Sheets-Sheet 1 United States Patent Office 3,761,268 Patented Sept. 25, 1973 3,761,268 SELF-DEVELOPING PHOTOGRAPHIC FILM ASSEMBLAGE Edwin H. Land, Cambridge, and Richard J. Chen, Winchester, Mass, assignors to Polaroid Corporation, Cambridge, Mass.

Filed May 5, 1972, Ser. No. 250,611 Int. Cl. G03c 1/48 US. Cl. 96-76 C 38 Claims ABSTRACT OF THE DISCLOSURE A photographic film assemblage of the self-developing type comprising a photosensitive layer on one of a pair of sheets including a rectangular area adapted to be exposed and processed by superposing the sheets and advancing them relative to and between a pair of juxtaposed pressure-applying members to distribute a viscous liquid processing agent in a thin layer between the sheets from the leading edge of the exposed area to the trailing edge thereof. The assemblage includes spacing layers at the lateral margins of the area, tapered in thickness from a maximum near the leading edge to a minimum near the trailing edge of the area. A preferred embodiment shown is a self-developing film unit comprising two rectangular sheets secured in face-to-face relation by a binding sheet secured to the surface of one of the sheets and having marginal sections folded around the lateral and trailing end edges of the sheets and secured to the margins of the other sheet. The binding sheet is formed with a rectangular opening through which a layer of photosensitive material between the sheets is exposed and/or a visible image formed between the sheets is viewed. The binding sheet includes a section tapered in thickness from at least the leading edge of the opening to at least the trailing edge of the opening for cooperating with the pressure-applying members to control the thickness of the layer of liquid and is formed of a uniformly thick support and a pigment-containing coating which is tapered in thickness.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to photographic film assemblages of the self-developing type in which a viscous liquid processing agent is spread in a thin layer between external, dimensionally stable layers of the film assemblage to process an exposed area of photosensitive layer to form an image and particularly, to film units of the type in which the dimensionally stable layers are retained in superposition prior to, during, and subsequent to exposure and processing by sheet-like, external binding means secured around and to at least the lateral edges of the dimensionally stable layers.

Description of the prior art Numerous forms of photographic, self-developing assemblages have been proposed in the prior art as well as being sold commercially including both roll film and individual film units. The type of film assemblage or unit with which the present invention is concerned generally comprises a pair of sheets, one of which serves as a support for a photosensitive image-recording medium and a rupturable container of a viscous liquid processing agent adapted to be distributed in a thin layer in contact with an exposed area of the photosensitive medium by superposing the sheets and advancing them between a pair of pressure-applying members to distribute the processing liquid between the sheets for permeation into the recording medium. The photosensitive sheet (carrying the photosensitive medium) and the other or second sheet may be separated or superposed during exposure, are superposed during processing, and may be separated or allowed to remain laminated to one another by the processing liquid subsequent to processing; or they may be retained in superposed relation prior to, during, and subsequent to exposure and processing. Film units of this latter type are disclosed, for example, in U.S. Pat. Nos. 3,415,644, 3,415,645, 3,415,646, 3,473,925, 3,550,515, 3,578,540, 3,589,904, 3,594,164, 3,607,285, 3,615,421, 3,615,436, 3,615,539, 3,615,540, 3,619,192, 3,619,193, 3,621,768, 3,652,281, and 3,652,282.

Whatever the basic format and structure of the film assemblage, it is important, particularly in film units of the type described in the aforementioned US. patents, to spread the processing liquid in a layer of uniformly predetermined thickness throughout the area exposed and procssed preferably to produce an image visible through one of the sheets. One approach to liquid spreading and spread thickness control is to employ juxtaposed pressure-applying members, particularly rollers, resiliently biased toward one another and move the film unit therebetween to first eject the liquid from a rupturable container attached to the sheets near the leading end of the area to be processed and then progressively spread the mass of ejected liquid toward the trailing end of this area and the sheets. Liquid spread thickness control is achieved by providing sheet-like spacing elements at least at the lateral margins of the sheets for separating the medial portions of the pressure-applying members and sheets in the area to be processed in order to provide space between the sheets in which the liquid is spread. Heretofore, such spacing means have taken the form of uniformly thick layers or sheets formed of such materials as paper, organic plastics, and metallic foil, or combinations thereof, in the form of sheets or layers having openings defining the image area or strips and/or combinations of strips and sheets adapted to define the area to be processed.

In the film unit structure described in the aforementioned patents, these spacing means are designed to perform a number of functions in addition to spread thickness control including masking of non-image areas e.g. forming a border, and securing the two sheets to one another at at least their lateral and trailing end margins. For this purpose, the spacing means take the form of a generally rectangular sheet formed with a rectangular exposure and/or viewing opening surrounded on at least three sides by lateral and trailing end marginal portions secured to one of the photosensitive and second sheets, folded around the lateral and trailing end edges of the sheets and secured to the other of the photosensitive and second sheets.

While this structure has proved essentially satisfactory for controlling the extent and thickness of the layer of processing liquid spread for permeation into the photosensitive material, in structures such as disclosed in many of the foregoing patents, particularly Pat. No. 3,619,192, for example, it has been found that the layer of processing liquid tends to vary in thickness from a minimum near the leading edge of the area to a maximum at the trailing edge of the area. This is particularly true when motor driven rollers are employed for advancing the film unit and effecting and spreading the processing liquid. This variation in spread thickness may range from fifteen to thirty percent of the average thickness of the layer of liquid so that in some areas there will be insufficient liquid while in other areas there will be an excess of liquid; and is believed to be due to a number of factors. Principal among these is variation in the speed of movement of the film unit between the pressure-applying members, the speed varying from a minimum near the leading end to a maximum near the trailing end of the film unit.

This, in turn, is attributed to the necessity for initially moving the thickest part of the film unit and the part offering the most resistance to initial movement, specifically, the container, between the pressure-applying members to eject a mass of viscous liquid from the container between the leading end portions of the superposed sheets. Secondly, the mass of liquid being advanced toward the trailing end of the film unit becomes smaller as it is advanced and absorbed thus resulting in a decrease in the resistance to film unit motion permitting higher speeds with the same applied force in turn resul ing in thicker liquid spreads. In other words, relatively slow movement of the film unit results in liquid spreads relatively thinner than with fast movement (see, for example, US. Pat. Nos. 3,604,329 and 3,589,262), so that when such a film unit is employed with motor driven spread rolls where the maximum driving force is limited, the speed and hence the spread thickness tend to vary.

SUMMARY OF THE INVENTION Objects of the invention are: to provide in photographic film assemblages or unit of the type described, novel and improved means for controlling the extent and thickness of the spread of the processing liquid to insure more uniform spread thickness; and, specifically, to provide improved means characterized by simplicity and inexpensiveness, for preventing tapering of the thickness of the layer of viscous processing liquid distributed in contact with the area, usually rectangular, to be processed.

These and other objects of the invention are realized by the provision of novel spacing means for cooperating with a pair of juxtaposed pressure-applying members during movement of the film assemblage therebetween to spread the viscous processing liquid. The spacing means include at least narrow layers located adjacent the edges of the area to be processed, extending in the direction of spreading and adapted to space apart the medial portions of the pressure-applying members during movement of the sheets of the film assemblage therebetween. The spacing layers which may be in the form of coatings and/ or sheet materials, are tapered from a maximum thickness near the leading end of the area over which the liquid is spread to a minimum thickness near the trailing end of this area.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the product possessing the features, properties and the relation of components which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view, partially in section, illustrating a typical film unit embodying the invention;

FIG. 2 is a plan view of a component of the film unit of FIG. 1; and

FIG. 3 is a sectional view taken substantially along the line 33 of FIG. 2.

Film assemblages or units constructed in accordance with the invention may be adapted to the performance of a number of different image-forming processes and particularly to the production of positive photographic prints, preferably in full color, produced by a diffusion transfer process in which a photographic image-recording medium including a photosensitive material such as a silver halide is exposed to form an image (latent) therein and is treated by wetting with a liquid processing agent to develop the image in the image-recording medium, form an imagewise distribution of transferrable image-forming substances and transfer the image-forming substances by diffusion to an image-receptive stratum in which they are immobilized to form a visible positive image.

A preferred embodiment of a film unit of this type includes all of the material and reagents required to produce a full color photographic print by a process such as disclosed in US. Pat. No. 2,983,606, and in many of the aforementioned US. patents. Such a film unit includes a photosensitive element comprising a silver halide emulsion and a dye developer, that is a dye which is a silver halide developing agent; an image-receptive layer of a dyeable material which may be carried on the same support as the photosensitive layer (see for example, Pat. Nos. 3,594,164 and 3,594,165); or on a separate support which is superposed with the image-recording medium, i.e. image-recording layer and support, at least during processing, (see for example, US. Pat. Nos. 3,415,644 and 3,415,646).

As noted in the aforementioned patents, the silver halide layer has associated therewith a dye image-providing material which provides an imagewise distribution of a processing composition diffusible image-forming substance as a function of exposure of its associated photosensitive silver halide such as the dye image-providing materials disclosed in the aforementioned patent numbers. Application of the liquid processing composition results in imagewise differential transfer of dye imageproviding material to a contiguous image-receptive element or layer providing dye image formation in such an element as a function of the point to point degree of photoexposure of the silver halide layer.

The processing liquid is generally quite viscous and contains a film-forming material in quantities sufiicient to provide a viscosity in excess of 1000 centipoises at a temperature of 20 C. and preferably of the order of 1000 to 200,000 centipoises at said temperature. This viscosity results in the formation of a thin layer of liquid as a pair of sheets between which the liquid has been introduced, are advanced between a pair of pressureapplying members. While the amount of variation in the thickness of the layer of liquid which can be tolerated without adversely effecting the visible image may vary depending on the physical structure and chemical composition of the various layers of the film unit and the function of the liquid processing agent, in many film unit structures, particularly those of the type disclosed in the aforementioned Patent No. 3,619,192, the thickness of the layer of processing liquid is required to be maintained within close tolerances throughout the area to be processed and in which the visible difiusion transfer image is formed. This necessity for uniform liquid distribution is, in part, a function of the film structure which requires the liquid to be distributed in a layer between the photosensitive layer and the image-receiving layer. The processing liquid performs another function in this particular film unit construction in which the photosensitive and imagereceiving sheets are maintained in superposition prior to, during, and subsequent to processing and the image-receiving sheet is transparent to permit viewing of the diffusion transfer image. This function is dual and is both to preprocessing when such processing takes place in the light outside of the camera in which the film is exposed, as well as to provide a pigment for the transfer image effe tively masking the underlying photosensitive layer and the image formed therein.

DESCRIPTION OF THE PREFERRED EMBODIMENT Reference is now made to FIG. 1 of the drawings wherein there is illustrated a photographic film unit 10 embodying the invention, the thickness of the material being exaggerated for purposes of clarity of illustration. Film unit 10 is essentially the same as the film unit described in the aforementioned Pat. No. 3,619,192 and comprises a photosensitive or image-recording sheet 12,

a second or image-receiving sheet 14, and a rupturable container 16 holding a quantity of processing liquid 18. Sheets 12 and 14 are preferably rectangular and are arranged in superposed face-to-face contact with their lateral edges in alignment. Sheet 14 is preferably longer than sheet 12 having a length exceeding the length of sheet 12 by at least the shorter dimension of container 16 of processing liquid 18. Container 16 is mounted on the extended portion of receiving element 14 adjacent the leading edge of photosensitive element 12 in position to discharge its liquid contents between the photosensitive and image-receiving elements at the leading edge of the latter.

Photosensitive and image-receiving elements 12 and 14 are secured to one another at their lateral and trailing end margins by a binding element 20 (the original shape of which is shown most clearly in FIG. 2) in the form of a generally rectangular sheet larger than the image-receiving element. Binding element 20 is in the general form of a frame having a large rectangular exposure opening 22 defining the extent of the area in which the image is produced in the film unit, surrounded by lateral edge portions 24, a trailing end portion 26 and a leading end portion 28. Binding element 20 is secured to the outer surface of image-receiving element 14 with the lateral edges of exposure opening 22 located substantially parallel with and equally spaced from the lateral edges of sheets 12 and 14. Lateral marginal portions 24 of the binding element are folded around the lateral edges of sheets 12 and 14 and secured to the lateral margins of element 12. Trailing end portion 26 of the binding sheet is folded around the trailing edges of sheets 12 and 14 and secured to the outer surface of sheet 12 near the trailing edge thereof.

Container 16 is mounted on the extended portion of element 14. The leading end portion 28 of binding element 24 extends at least over sheet 14 and preferably around the leading edge thereof where it is secured at its leading end margin to container 16 to retain the container against the image-receiving element. In an alternative embodiment, the container 16 may be secured to element 14 so that bindin element 20 need only extend to the leading edge of element 14. The preferred form of film unit shown is adapted to produce a reflection print surrounded by a white border and viewed against a white background so that binding element 20 is formed of an opaque white material to provide an aesthetically pleasing product as well as to prevent exposure of the photosensitive material by light admitted at or near the edges of sheets 12 and 14 if and as the film unit is moved directly into the light from between the pressure-applying members during processing.

Container 16 is of the type shown in US. Pat. No. 2,543,181, and is formed by folding a rectangular blank of a finid impervious sheet material medially and sealing the marginal sections of the blank to one another to form a cavity for containing processing liquid 18. Such containers are well known, have been in use for many years, and include longitudinal, marginal sections 30 at which the seal is weaker than the end seals so that upon the application of a compressive force to the walls of the container in the region of the liquid-filled cavity, there will be generated within the liquid hydraulic pressure sufficient to separate longitudinal and marginal sections 30 throughout the major portion of their length to form a discharge mount at least equal in length to the cavity and the width of opening 22 through which processing liquid 18 is discharged. Container 16 is mounted on sheet 14 with the edges of marginal sections 30 located adjacent the leading edge of sheet 12. A binding strip 32 is secured in overlapping relation to the leading edge of element 12 and longitudinal marginal section 38 of container 16 for cooperating with sheet 14 to form a passage for conducting the liquid from the container between the sheets at the leading end margin of sheet 12.

The preferred embodiment of the film unit is adapted to be processed by advancing the film unit, leading end foremost, between a pair of juxtaposed pressure-applying members prferably in the form of cylindrical rollers which may be rotated manually or by a motor for moving the film unit therebetween. The pressure-applying members or rollers initially pass over the container ejecting its liquid contents as an elongated mass between the leading end portion of sheet 12 and the facing adjacent portion of sheet 14. Continued movement of the film unit relative to and between the rollers results in spreading of the processing liquid as a thin layer between the sheets at least over the area defined by opening 22 in binding element 20. In order to insure distribution of processing liquid in a layer of the desired thickness over the entire area defined by opening 22, excess processing liquid 18 is provided in container 16 and provision is made within the film unit for collecting and retaining this excess prooessing liquid. A variety of liquid collecting and retaining structures are shown in many of the aforementioned patents including, for example, a spacing member 34 secured between the trailing edge portion of photosensitive element 12 and a trailing edge portion 26 of binding element 10 adhered to sheet 12. Spacing element 34 may take the form of a comb-shaped strip or a strip formed with perforations designed to space apart the pressureapplying members as they pass over the trailing end of the film unit and provide spaces within the trailing end of the film unit for collecting and retaining excess processing liquid overrun.

As previously indicated, the preferred form of film unit shown is adapted to be advanced from between pressureapplying members from the camera or other apparatus in which it is exposed into the light where processing continues to completion. The processing liquid and/ or layers of the film unit contain agents for preventing or at least inhibiting further exposure of the photosensitive imagerecording material and/or desensitizing the image-recording material so that it is not subjected to an image-forming exposure as it emerges into the light. In the particular film unit construction shown, the processing liquid is spread between the image-recording medium and the image-receiving layer which is carried on a transparent support in order to permit exposure of the photosensitive material and viewing of the diffusion transfer image formed in or on the image-receiving layer. Accordingly, the processing liquid not only comprises the agents necessary to produce a dye transfer image, e.g., an aqueous alkaline solution with a pH at which dye developers associated with the silver halide layers are soluble and diffusible, but also contains a light-reflecting agent -in a quantity sufficient to mask the dye developers retained in the image-recording layer (laminated thereto) subsequent to processing. In the preferred embodiment, the lightrefiecting agent and an optical filter agent as described in US. Pat. No. 3,647,437 will be present in the layer of liquid spread between the transparent sheet 14 and photosensitive sheet 12 which may be light opaque, in a concentration sufficient to inhibit, if not prevent, exposure of the image-recording medium by actinic radiation transmitted by transparent sheet 14. It is for these latter two reasons as well as to achieve uniform processing that it is important that the layer of processing liquid have a thickness maintained within relatively close tolerances. Typically, the processing liquid is initially distributed in a layer having a thickness of the order of 0.003 to 0.004 inch which is reduced as the solvent, i.e. water, is absorbed, to a layer having a thickness of the order of 0.002 inch. The light-reflecting agent is selected for its suitability as a background for viewing the dye transfer image formed in the dyeable polymeric image-receiving layer as well as for its opaque properties and its freedom from interference with the formation and color integrity of the dye transfer image. This agent should be aesthetically pleasing and should not provide a noisy background that may degrade the image or detract from the information content thereof. For this purpose, suitable light-reflecting agents are those providing a white background such as conventionally employed to provide backgrounds for photographic reflection prints and having optical properties particularly suited for the reflection of incident radiation.

As examples of suitable light-reflecting agents, mention may be made of barium sulfate, zinc oxide, titanium dioxide, barium stearate, silver flake, silicates, alumina, zirconium, acetyl acetate, sodium Zirconium sulfate, and the like. Titanium dioxide is especially preferred for its whiteness and high reflection properties, and formulations of processing liquids including titanium dioxide are given in various of the aforementioned patents.

As is well known in the art and noted in the aforementioned patents, particularly patent No. 3,619,192, the depth of the layer of processing liquid initially spread between the sheets 12 and 14 is controlled by providing narrow strips or layers at the lateral margins of the area in which the lquid is spread and the image is formed. Whether the film assemblage comprises a plurality of image areas arranged in coiled strip form or a single exposure film unit, such strips or layers may be located between the sheets as shown, for example, in US. Patent No. 2,627,460 and as will be noted from an examination of the various photographic film products (both in roll and film unit form) sold by Polaroid Corporation, in which spread control is achieved by a masking sheet located between the photosensitive and image-receiving sheets. In the preferred embodiment of the invention illustrated, marginal portions 24 of binding element 20 function to control the thickness of the layer of processing composition by engaging the end portions of the pressureapplying rollers and separating the medial portions thereof sufficiently to provide a space between sheets 12 and 14 in which the layer of processing liquid is distributed.

As previously noted, when processing a film assemblage or unit of the type incorporating the present invention, the leading end portion of the film unit which includes the container of processing liquid constitutes one of the thicker portions of the film unit offering substantially more resistance to movement between a pair of pressureapplying members than the portion of the film unit in the region of the urea defined by opening 22 and adapted to be processed. Thus, whether the film assemblage be moved manually or by a motor driven system, there is more resistance to movement during the beginning of spreading so the speed of movement tends to increase throughout the spreading process resulting in a minimum thickness spread near the leading edge of the exposed area and layer of liquid, to a maximum thickness spread near the trailing edge of the exposed area and layer of liquid. Not only does film assemblage thickness contribute to this problem, but it is further aggrevated by the fact that the liquid is spread by advancing a mass thereof between the sheets and this mass descreases in volume during the spreading thereby resulting in a commensurate decrease in the resistance to movement of the film unit between the pressure-applying members.

The invention is concerned with a novel and improved structure for achieving a uniform thickness layer of processing liquid rather than a layer of tapered thickness and the novel approach is to taper the spread thickness control components of the film assemblage opposite to the direction of taper that would be expected of the layer of processing liquid. This tapering is illustrated somewhat schematically in FIGS. 2 and 3. FIG. 2 shows a sequence of connected binding sheets 20 adapted to be severed from one another along the broken lines designated 40 which form the lateral edges of the individual binding sheets. The edges of the elongated strip of binding sheets shown in FIG. 2 define the leading and trailing end edges of each corner of each binding sheet 20 is cut off at approximately a 45 angle to prevent overlapping of the sheet material when the marginal portions are folded around the edges of sheet 14 and secured to the margins of sheet 12 and the margin of container 16. In embodiments such as roll film in which a mask is employed between the sheets to control the image area as well as spread thickness, a mask sheet similar to the binding sheet shown may be employed, the principle difference being that the lateral edges of the sheet will be tapered longitudinally while the arrangement of openings will differ to provide wide trailing and leading end portions.

The binding sheet 20 as illustrated in FIG. 3, comprises a dimensionally stable support sheet 48 on which is coated a multiple strata layer 50. Sheet 48 is of substantially uniform thickness, e.g. of the order of 1.0 to 1.5 mils, and may be formed of a multiple ply material composed, for example, of outer strata of thin capacitor tissue paper each approximately 0.3 mil thick adhered to opposite sides of a polyester film approximately .5 mil thick. A sequence of coatings are applied to support 48 to form layer 50 which is of uniform maximum thickness from the leading edge of element 20 to near the leading edge of opening 22 where it commences to taper uniformly to a minimum thickness approximately midway between the trailing edge of opening 22 and the trailing edge of binding element 20. Coating 50 essentially comprises a white pigment such as titanium dioxide in a polymeric binder designed to perform both mechanical and aesthetic functions. The mechanical function, as noted, is to control the spread thickness while the aesthetic function is to provide a pleasing white border surrounding the visible image.

A typical binding sheet 20 is illustrated by way of example in FIGS. 2 and 3 together with pertinent dimensions. The binding sheet is designed for use with a film unit having an overall dimension of approximately 4.25 by 3.5 in. with an image area approximately 3.14 in. square. The processing liquid is distributed within the film unit between sheets 12 and 14 by rapidly advancing the film unit between a pair of motor driven pressureapplying rollers, the speed of advancement being of the order of 10 inches per second, to form a layer of processing liquid approximately 0.004 in. thick. It has been found that the use of a uniform thickness binding element 20 may result in tapering of the layer of processing liquid by as much as 0.001 in. or twenty-five percent and that variations in spread thickness due to mechanical factors such as deviations in spread roll concentricity, spread roll speed, gear chatter in the speed roll drive system, and the like, also contribute measurably to variations in the thickness of the layer of processing liquid spread between the sheets. However, it has been found that tapering of the marginal sections 24 of sheet 20 not only substantially eliminates the end to end taper of the layer of processing liquid, but also reduces or eliminates the variations in spread thickness resulting from mechanical factors such as noted above, thus producing a substantially uniformly thick processing liquid layer and a better quality and more pleasing image.

In the example shown, the support sheet 48 is coated on one side with a multiple strata layer basically comprising a layer or layers of titanium dioxide pigment applied in a polyester binder and overcoated with a clear lacquer consisting, for example, essentially of nitrocellulose and a wax modifier, for preventing dirt accumulation and cracking, and functioning as a friction-reducing coating. Typically, a base 1.24 mils thick is coated on one side to taper from a maximum overall thickness of 1.98 mils near the leading edge of opening 22 to a mini mum thickness of 1.66 mils just beyond the trailing edge of the opening. A heat seal coating is applied to the opposite side of support sheet 48 to provide for lamination of sheet 20 to sheets 12 and 14. The heat-sealed coating consisting, for example, essentially of ethylene vinyl acetate, increases the maximum overall thickness to approximately 2.2 mils and the minimum thickness to approximately 1.92 mils thus providing a total difference in thickness between the ends of the tapered section of 0.28 mils. In the example given, the desired taper is 0.30 mils with a tolerance of 10.003 mils., or approximately 10 times the length of opening 22. The difference in thickness between the ends of the tapered portions in this illustration is therefore approximately of the maximum thickness.

Sheet is initially provided as shown in FIG. 2, as a part of an elongated strip coated as shown and described, is cut along the broken lines, is adhered to sheet 14, and is folded around the lateral and trailing end edges of sheet 14 and adhered to the lateral and trailing end margins of sheet 12. In this way, the taper of the binding sheet is effectively doubled inasmuch as two layers (adhered to sheets 12 and 14) of the binding sheet engage the pressure-applying rolls as the film unit is moved therebetween. Thus, the taper is effectively increased to approximately 0.6 mils and this has been found effective to produce the desired uniformly thick spread.

The tapered spread thickness control means may be provided by a number of techniques, the preferred method being by a gravure process in which the depressions or cells in the gravure rolls are varied in depth according to the layer thickness taper desired in accordance with the procedure disclosed and claimed in copending and commonly assigned US. patent application of John J. Dennis, Jr. et al., Ser. No. 303,685, filed Nov. 6, 1972. It will be noted from FIGS. 2 and 3 that the trailing end portion of sheet 20 is provided with a stripe along the trailing edge comprising a portion of layer 50 and being a maximum thickness. The purpose of this stripe, designated 50a is to enable coiling of an elongated strip of sheet 20 by providing at least lateral margins which are of equal thickness. Stripe 50a has no effect on the spreading of the processing liquid inasmuch as it is located beyond the trailing edge of opening 22 which defines the area in which spread thickness is critical.

While the white pigment layer which provides the tapered strips adjacent the lateral edges of the superposed sheets of the film unit is illustrated as a layer on a binding sheet which also functions to provide a border around the visible transfer image, it should be understood that the tapered layer may take other forms including, for example, narrow strips provided with tapered coatings or coatings applied directly to either or both of the photo sensitive and second sheets such as shown in the copencling US. application of Rogers B. Downey, Ser. No. 102,- 447, filed Dec. 29, 1970. Alternatively, in film assemblages of both the film unit and roll film type in which a transfer image, usually a reflection print, is formed on an image-receiving sheet which is separated from the photosensitive sheet, the support of the image-receiving sheet is usually paper or a laminate coated with a white reflective material such as titanium dioxide so that it would be considered to fall within the scope of the present invention to build up and taper one or several of the coatings or'layers comprising the receiving sheet in accordance with the teachings herein.

It will be seen from the foregoing that the present invention achieves its basic objective of providing a film structure assuring uniform, processing liquid layer spread thickness utilizing a relatively simple, inexpensive, and easily fabricated structure. This structure is essentially a tapered layer which, in the preferred embodiment described, performs the aesthetic function of providing a well-defined, aesthetically pleasing, white border around the visible image as well as the mechanical function of insuring uniform spread thickness.

Since certain changes may be made in the above prodnot without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is: 1; In a photographic film assemblage of the self-developing type including a layer of photosensitive imagerecording material supported on one of a pair of sheets and including at least a generally rectangular area adapted to be exposed and processed by a viscous liquid processing agent distributed in a thin layer between the sheets from the leading edge of the exposed area toward the trailing edge thereof, the improvement comprising:

spacing means for cooperating with means for spreading a voscous processing liquid in a thin. and substantially uniformly thick layer between the sheets over said area for permeation into said image-recording material; said spacing means including at least a pair of relatively narrow spacing layers mounted on at least one of said sheets adjacent the lateral edges of said area of said photosensitive material to be processed;

said spacing layers being tapered from a maximum thickness near the leading end of said area to be processed to a minimum thickness near the trailing end of said area.

2. A photographic film assemblage according to claim 1 wherein said spacing layers are tapered substantially uniformly and are of substantially equal thickness in laterally aligned areas.

3. A photographic film assemblage according to claim 2 further including a second pair of said spacing layers mounted on the lateral margins of the other of said sheets in alignment with the first mentioned spacing layers mounted on said one of said sheets.

4. A photographic film assemblage according to claim 2 wherein said spacing layers have edges substantially parallel with one another.

5. A photographic film assemblage according to claim 1 wherein each of said spacing layers includes a pigmentcontaining stratum tapered in thickness.

6. A photographic film assemblage according to claim 5 wherein said pigment-containing stratum is coated on a sheet-like support element to form a dimensionally stable spacing layer of substantially uniform thickness adhered to said one sheet.

7. A photographic film assemblage according to claim 6 wherein each of said spacing layers includes at least a strip of sheet material secured around and to the lateral margins of the first mentioned sheets.

8. A photographic film assemblage according to claim 6 wherein said pigment-containing layers include tapered portions at least equal in length to said area of said photosensitive material adapted to be processed, and the difference in thickness between the ends of said tapered portions is approximately fifteen percent of the maximum thickness of said spacing layers.

9. A photographic film assemblage according to claim 6 wherein said spacing layer includes a generally rectangular section formed with a rectangular opening defined on two sides by lateral portions coated with said pigment-containing strata tapered in thickness.

'10. A photographic film assemblage according to claim 6 wherein said spacing layer includes an elongated support element formed with a plurality of spaced rectangular openings defining said areas to be processed and said pigment-containing stratum is coated thereon and tapered in thickness adjacent opposite sides of each of said openmgs.

11. A photographic film unit including first and second rectangular sheets arranged in superposed relation and including an intermediate layer of a photosensitive material having an area adapted to be exposed through one of said sheets and treated to produce an image by a viscous liquid processing agent distributed in a layer between said sheets, a rupturable container of a viscous liquid processing agent secured to said sheets in position to discharge its liquid contents between the sheets for subsequent spreading from the leading edge of said area adapted to be exposed and processed, toward the trailing edge of said area 'by and in response to the application of compressive pressure to said container and said sheets commencing with said container and progressing toward the trailing end of said area, the improvement comprising:

sheet-like binding means secured around and to at least the lateral margins of said sheets adjacent the sides of said area for retaining said sheets in faceto-face relation during distribution of said processing liquid and controlling the thickness of said layer of said liquid distributed over said area, said binding means being tapered from a maximum thickness in the region of the leading edge of said area to a minimum thickness in the region of the trailing edge of said area.

12. A photographic film unit according to claim 11 wherein said binding means are tapered uniformly.

13. A photograpihc film unit according to claim 12 wherein said binding means are tapered from approximately said leading edge of said area to a transverse line located beyond said trailing edge of said area.

14. A photographic film unit according to claim 11 wherein said binding means comprise a substantially uniformly thick sheet material coated with a layer tapered in thickness and including at least a stratum containing a pigment.

15. A photographic film unit according to claim 14 wherein said binding means are substantially opaque to visible light.

16. A photographic film unit according to claim 15 wherein said pigment-containing stratum is white.

17. A photographic film unit according to claim 16 wherein said pigment-containing stratum is tapered in thickness.

18. A photographic film unit according to claim 11 wherein the difference in thickness between the ends of the tapered portions of said binding means is approximately fifteen percent of the maximum thickness of the said binding means.

19. A photographic film untt according to. claim 11 wherein the difference in thickness between the ends of the tapered portions of said binding means is approximately times the length of said area.

20. A photographic film unit according to claim 19 wherein said difference in thickness is approximately fifteen percent of the maximum thickness of said binding means.

21. A photographic film unit as defined in claim 11 wherein said binding means comprise a generally rec.- tangular binding sheet secured in face-to-face relation to one of said sheets and having lateral and trailing end marginal portions folded around the lateral and trailing end edges of one of said sheets and secured to the margins of the other of said sheet, said binding sheet being formed with a rectangular opening defining said area adapted to be exposed and processed and including a section extending from side to side thereof tapered in thickness, said tapered section ranging in thickness from a maximum in the region of the leading edge of said opening to a minimum in the region of the trailing edge of said opening.

22. A photographic film unit as defined in claim 21 wherein said tapered section of said binding sheet is tapered substantially uniformly.

23. A photographic film unit as defined in claim 22 wherein said binding sheet includes a leading end marginal section at which said tapered section begins and a trailing end marginal section at which said tapered section ends.

24. A photographic film unit as defined in claim 22 wherein said binding sheet is tapered from a transverse line coinciding approximately with said leading edge of said opening to another transverse line located approximately midway between said trailing edge of said opening and the trailing edge of said binding sheet.

25. A photographic film unit as defined in claim 21 wherein said binding sheet comprises a substantially uniformly thick support sheet coated with a layer tapered in thickness and including at least a stratum containing a pigment.

26. A photographic film unit as defined in claim 25 wherein said binding sheet is substantially opaque to visible light.

27. A photographic film unit as defined in claim 26 wherein said pigment-containing stratum is substantially white.

28. A photographic film unit as defined in claim 25 wherein said pigment-containing stratum is tapered in thickness.

29. A photographic film unit as defined in claim 21 wherein the difference in thickness between the ends of said tapered section is approximately fifteen percent of the maximum thickness of said binding sheet.

30. A photographic film unit as defined in claim 21 wherein the difference in thickness between the ends of said tapered section is approximately 10- times the length of said opening.

31. A photographic film unit as defined in claim 30 wherein said difference in thickness is approximately fifteen percent of the maximum thickness of said binding sheet.

32. For use in a photographic film unit, a generally rectangular binding sheet formed with a medial rectangular opening comprising, in combination:

a support sheet; and

a pigment-containing coating completely covering at least one side of said support sheet, said coating including a medial section extending from sid to side of said sheet and tapering substantially uniformly from a maximum thickness near one end edge of said opening to a minimum thickness near the opposite end edge of said opening.

33. A binding sheet according to claim 32 wherein said coating includes end sections of substantially uniform maximum thickness extending from the ends of said tapered section to the end edges of said support sheet.

34. A binding sheet according to claim 32 wherein the difference in thickness between the ends of said tapered section is approximately fifteen percent of the maximum thickness of said binding sheet.

35. A binding sheet according to claim 32 wherein the difierence in thickness between the ends of said tapered section is approximately 10- times the length of said opening.

36. A binding sheet according to claim 35 wherein said difference in thickness is approximately fifteen percent of the maximum thickness of said binding sheet.

37. A binding sheet according to claim 32 wherein said binding sheet is substantially opaque to visible light.

38. A binding sheet according to claim 37 wherein said pigment-containing coating is substantially white.

References Cited UNITED STATES PATENTS 3,604,329 9/1971 Land -13 2,627,460 2/1953 Land 96-29 3,619,192 11/1971 Land 96-76 C NORMAN G. TORCHIN, Primary Examiner J. L. GOODROW, Assistant Examiner US. Cl. X.R. 95-13 

